Calculator Inputs
Example Data Table
These sample values show how different chamber sizes and fan selections affect purge time and design status.
| Case | Volume | Opening Area | Target Velocity | Fan Flow | Expected Result |
|---|---|---|---|---|---|
| Small bench chamber | 2.16 m³ | 0.45 m² | 0.45 m/s | 900 m³/h | Usually adequate for light extraction. |
| Medium process chamber | 6.91 m³ | 0.90 m² | 0.50 m/s | 2400 m³/h | Often acceptable with moderate safety allowance. |
| Large enclosure | 18.00 m³ | 1.80 m² | 0.60 m/s | 4200 m³/h | May need a larger fan or smaller opening. |
Formula Used
Chamber volume: V = L × W × H
Opening area: A = opening width × opening height
Flow for face velocity: Qface = A × target velocity × 3600
Flow for air changes: Qach = chamber volume × desired ACH
Recommended flow: Qrec = max(Qface, Qach) × (1 + safety factor) ÷ (1 - leakage allowance)
Actual ACH: ACHactual = existing fan flow ÷ chamber volume
Purge time: Time = required purge cycles ÷ actual ACH × 60
Duct pressure loss: ΔP = (f × L ÷ D + K) × ρ × v² ÷ 2
Estimated concentration: C = emission rate ÷ airflow per minute
These formulas are planning estimates. Final ventilation design should also consider contaminant type, capture behavior, filter loading, fan curves, code requirements, and professional safety review.
How to Use This Calculator
- Enter the internal length, width, and height of the extraction chamber.
- Enter the open face size where air enters the chamber.
- Add the desired face velocity and air change target.
- Enter the fan flow available from your selected exhaust fan.
- Add duct diameter, duct length, friction factor, and loss coefficient.
- Use the safety factor and leakage allowance for conservative sizing.
- Add emission rate and limit when a concentration check is needed.
- Press the calculate button and review the result above the form.
- Use CSV or PDF buttons to save the calculation report.
Extraction Chamber Planning Guide
Why Airflow Matters
An extraction chamber depends on controlled airflow. Air must move into the chamber, across the source, and out through the exhaust path. If the airflow is too low, vapors, fumes, dust, or mist can escape. If the airflow is too high, the system may waste energy. High velocity can also disturb light materials inside the chamber. A balanced design protects users and supports stable operation.
Chamber Volume and Purge Time
Chamber volume controls the amount of air inside the enclosure. Larger chambers need more flow to reach the same air change rate. Purge time estimates how long the fan needs to replace chamber air. Many users choose several purge cycles before opening the chamber. This calculator estimates purge time from fan flow and chamber volume. It also shows actual air changes per hour.
Face Velocity and Capture
Face velocity is the air speed through the chamber opening. It is useful when the chamber has a door, window, or access face. A larger opening needs more airflow to maintain the same velocity. Smaller openings are easier to control. The calculator compares the airflow needed for face velocity with the airflow needed for air changes. It then uses the larger value as the base design flow.
Duct Loss and Fan Selection
A fan must overcome pressure loss in the duct system. Long ducts, small ducts, bends, hoods, filters, and dampers increase resistance. This tool estimates duct velocity, dynamic pressure, and total pressure loss. It also estimates fan power from airflow, pressure, and efficiency. Use these values when comparing fan curves. A fan rated at free air may deliver much less flow after duct losses.
Safety Margin and Practical Review
Real systems rarely perform exactly like drawings. Leakage, filter loading, poor sealing, and flow imbalance can reduce capture. That is why a safety factor is useful. The calculator also adds a leakage allowance. These features help create a more conservative recommendation. The final design should still be checked with measurements, smoke tests, and applicable safety guidance.
FAQs
1. What does this extraction chamber calculator estimate?
It estimates chamber volume, required airflow, purge time, face velocity, pressure loss, fan power, and concentration status using practical ventilation inputs.
2. Which airflow value should I trust most?
Use the recommended fan flow. It compares face velocity demand and air change demand, then adds safety and leakage allowances.
3. What is purge time?
Purge time is the estimated time required to replace chamber air by a selected number of air changes using the available fan flow.
4. Why does opening size matter?
A larger opening needs more airflow to maintain the same face velocity. Reducing opening size can improve capture performance.
5. What does the loss coefficient mean?
It represents minor losses from bends, entries, exits, dampers, filters, and fittings. Higher values increase estimated pressure loss.
6. Can this calculator replace a professional design?
No. It provides planning estimates. Critical systems should be reviewed by qualified ventilation, safety, or industrial hygiene professionals.
7. Why include a safety factor?
A safety factor helps account for imperfect sealing, fan aging, filter loading, measurement error, and future operating changes.
8. Why is my fan marked undersized?
The entered fan flow is lower than the recommended flow after face velocity, air changes, safety factor, and leakage allowance are considered.